In a dark bar or nightclub, it can be difficult to recognize conventional liquor bottles and differentiate one from another. Most liquor bottles all have the same general shape and rely on labels and external lighting for recognition. Some bars include special lighting to help illuminate their array of liquor bottles.
In addition, conventional liquor bottles come with a sealed screw cap that the bartender removes and replaces with a conventional pour spout. Typically, when one bottle of a certain liquor is empty, the bartender will pull the pour spout out of the empty bottle and reinsert it into a full bottle. When a partially empty liquor bottle is not in use, it typically sits on a shelf with a pour spout exposed for long periods of time, often for days and weeks. Over time, the pour spouts become crusty and dirty, and fruit flies often climb into the exposed opening of the pour spout.